The leading role of energy in the metabolic pathway depends on the process, the essence of which is oxidative phosphorylation. Nutrients are oxidized, forming the energy that the body stores in the mitochondria of cells like ATP. Every form of earthly life has its own favorite nutrients, but ATP is a universal compound, and the energy that oxidative phosphorylation produces is stored up in order to use it for metabolic processes.
Bacteria
More than three and a half billion years ago, the first living organisms appeared on our planet. Life was born on Earth due to the fact that the emerging bacteria - prokaryotic organisms (without a nucleus) were divided into two types according to the principle of respiration and nutrition. By respiration - by aerobic and anaerobic, and by nutrition - by heterotrophic and autotrophic prokaryotes. This reminder is unlikely to be unnecessary, because oxidative phosphorylation cannot be explained without basic concepts.
So, prokaryotes with respect to oxygen (physiological classification) are divided into aerobic microorganisms, which do not care about free oxygen, and aerobic, whose vital activity depends entirely on its presence. It is they who carry out oxidative phosphorylation, being in an environment saturated with free oxygen. This is the most widespread metabolic pathway with high energy efficiency compared to anaerobic fermentation.
Mitochondria
Another basic concept: what is mitochondria? This is the energy cell battery. Mitochondria are located in the cytoplasm and there are an incredible number of them - in the muscles of a person or in his liver, for example, cells contain up to one and a half thousand mitochondria (just where the most intense metabolism occurs). And when oxidative phosphorylation occurs in the cell, this is the “handiwork” of mitochondria, they also store and distribute energy.
Even mitochondria do not depend on cell division, they are very mobile, move freely in the cytoplasm when they need it. They have their own DNA, and therefore they are born and die on their own. Nevertheless, the life of the cell depends entirely on them, without mitochondria it does not function, that is, life is truly impossible. Fats, carbohydrates, proteins are oxidized, resulting in the formation of hydrogen atoms and electrons - reducing equivalents, which then follow the respiratory chain. This is how oxidative phosphorylation occurs; its mechanism, it would seem, is simple.
Not so easy
The energy produced by mitochondria turns into another, which is the energy of the electrochemical gradient purely for protons that are on the inner membrane of the mitochondria. It is this energy that is necessary for the synthesis of ATP. And this is exactly what oxidative phosphorylation is. Biochemistry is a fairly young science, only in the middle of the nineteenth century were granules of mitochondria found in the cells, and the process of obtaining energy was described much later. It was monitored how trioses formed through glycolysis (and most importantly pyruvic acid) produce further oxidation in the mitochondria.
Trioses use the energy of cleavage, from which CO 2 is released , oxygen is consumed and synthesizes a huge amount of ATP (adenosine triphosphoric acid, and what it is - people who are interested in bodybuilding are especially well aware). All of the above processes are closely associated with oxidative cycles, as well as the respiratory chain that carries electrons. Thus, oxidative phosphorylation occurs in cells, synthesizing “fuel” for them - ATP molecules.
Oxidative cycles and the respiratory chain
In the oxidation cycle, tricarboxylic acids liberate electrons, which begin their journey along the electron transport chain: first to coenzyme molecules, here NAD is the main thing (nicotinamide adenine dinucleotide), and then the electrons are transferred to the ETZ (electrotransport chain) until they combine with molecular oxygen and do not form a water molecule. Oxidative phosphorylation, the mechanism of which is briefly described above, is transferred to another site of action. This is the respiratory chain - protein complexes embedded in the inner membrane of mitochondria.
It is here that the climax occurs - the conversion of energy through a sequence of oxidation and the restoration of elements. The three main points of the electric transport chain where oxidative phosphorylation occurs are of interest here. Biochemistry examines this process very deeply and carefully. Perhaps a new cure for aging will someday be born from here. So, at three points of this chain, ATP is formed from phosphate and ADP (adenosine diphosphate is a nucleotide that consists of ribose, adenine and two portions of phosphoric acid). That is why the process has received such a name.
Cell respiration
Cellular (aka tissue) respiration and oxidative phosphorylation are the stages of the same process in the aggregate. Air is used in every cell of tissues and organs, where the breakdown products (fats, carbohydrates, proteins) are broken down, and this reaction generates energy stored in the form of macroergic compounds. Normal pulmonary respiration differs from tissue respiration in that oxygen enters the body and carbon dioxide is removed from it.
The organism is always active, its energy is spent on movement and growth, self-reproduction, irritability and many other processes. It is for this that oxidative phosphorylation in mitochondria occurs. Cellular respiration can be divided into three levels: the oxidative formation of ATP from pyruvic acid, as well as amino acids and fatty acids; acetyl residues are destroyed by tricarboxylic acids, after which two molecules of carbon dioxide and four pairs of hydrogen atoms are released; Electrons and protons are transported to molecular oxygen.
Additional mechanisms
Breathing at the cellular level provides the formation and replenishment of ADP directly in the cells. Although the body can replenish with adenosine triphosphoric acid in another way. For this, additional mechanisms exist and, if necessary, are included, although not as effective.
These are systems in which oxygen-free decomposition of carbohydrates occurs - glycogenolysis and glycolysis. This is no longer oxidative phosphorylation, the reactions are somewhat different. But cellular respiration cannot stop, because in its process very necessary molecules of the most important compounds are formed, used for a wide variety of biosyntheses.
Forms of energy
When electrons are transferred to the mitochondrial membrane, where oxidative phosphorylation occurs, the respiratory chain from each of its complexes directs the released energy to move protons through the membrane, that is, from the matrix into the space between the membranes. Then a potential difference is formed. Protons are positively charged and located in the intermembrane space, while negatively charged ones act from the mitochondrial matrix.
When a certain potential difference is reached, the protein complex returns protons back to the matrix, turning the energy received into a completely different one, where oxidative processes are coupled with synthetic processes - phosphorylation of ADP. During the entire period of oxidation of substrates and pumping of protons through the mitochondrial membrane, ATP synthesis does not stop, that is, oxidative phosphorylation.
Two kinds
Oxidative and substrate phosphorylation are fundamentally different from each other. According to modern concepts, the most ancient forms of life were able to use only substrate phosphorylation reactions. For this we used organic compounds existing in the external environment through two channels - as a source of energy and as a source of carbon. However, such compounds in the environment gradually dried up, and already emerging organisms began to adapt, look for new sources of energy and new sources of carbon.
So they learned to use the energy of light and carbon dioxide. But until this happened, the organisms released energy from the oxidative processes of fermentation and also stored it in ATP molecules. This is called substrate phosphorylation when the soluble enzyme catalysis method is used. The fermentable substrate forms a reducing agent, which transfers electrons to the desired endogenous acceptor - acetone, acetaldehyde, pyruvate and the like, or H 2 - hydrogen gas is released.
Comparative characteristics
Compared to fermentation, oxidative phosphorylation has a much higher energy yield. Glycolysis gives a total yield of ATP into two molecules, and from thirty to thirty-six are synthesized during the process. The transfer of electrons to acceptor compounds from donor compounds occurs through oxidative and reduction reactions that generate energy stored as ATP.
Eukaryotes carry out these reactions with complexes of proteins that are localized inside the mitochondrial membrane of the cell, and prokaryotes work outside - in its intermembrane space. It is this complex of bound proteins that makes up the ETC (electron transport chain). Eukaryotes in their composition have only five protein complexes, and prokaryotes - many, and they all work with a variety of electron donors and their acceptors.
Pairing and disconnecting
The oxidation process creates an electrochemical potential, and with the phosphorylation process this potential is used. This means that conjugation is ensured, otherwise - the binding of phosphorylation and oxidation processes. Hence the name - oxidative phosphorylation. The electrochemical potential necessary for pairing is created by three complexes of the respiratory chain - the first, third and fourth, which are called conjugation points.
If the inner mitochondrial membrane is damaged or its permeability from the activity of disconnectors increases, this will certainly cause the electrochemical potential to disappear or decrease, and then the phosphorylation and oxidation processes will separate, that is, termination of ATP synthesis. The phenomenon when the electrochemical potential disappears is called the separation of phosphorylation and respiration.
Disconnectors
The state when the oxidation of substrates continues, but phosphorylation does not occur (that is, ATP is not formed from and ADP), is a separation of phosphorylation and oxidation. This happens when disconnectors interfere with the process. What are they and what are the results striving for? Suppose ATP synthesis is greatly reduced, that is, it is synthesized in a smaller amount, and the respiratory chain functions. What happens to energy? It stands out as heat. Everyone feels this during an illness with fever.
Temperature? So, the disconnectors worked. For example, antibiotics. These are weak acids that dissolve in fats. Penetrating into the intermembrane space of the cell, they diffuse into the matrix, dragging the bound protons behind them. For example, hormones secreted by the thyroid gland, which contain iodine (triiodothyronine and thyroxine), have an uncoupling effect. If the thyroid gland is hyperfunctioning, the condition of the patients is terrible: they lack ATP energy, they consume a lot of food, because the body requires a lot of substrates for oxidation, but they lose weight because most of the energy received is consumed in the form of heat.